<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>结构伪类选择器</title>
    <style>
        :root, body{
           height: 100%;
           background: yellow;
        }
    </style>
</head>
<body>
</body>
</html>